This application is based on and claims the priority under 35 U.S.C. xc2xa7119 of German Patent Application 101 16 479.3, filed on Apr. 3, 2001, the entire disclosure of which is incorporated herein by reference.
The invention relates to a method and a control arrangement for actuating and controlling a flap that is pivotally connected to the rotor blade of a helicopter, using a piezoelectric actuator, a force transmitting linkage connecting the actuator to the flap, and a control circuit arrangement that controls the actuator.
The rotor system of a helicopter is the cause of the noise and the vibrations in the cabin. Simultaneously, the rotor system also generates a high exterior noise level, especially during the landing approach flight. These noise emissions and vibrations cause a drastic reduction of comfort for the helicopter passengers and are disadvantageous for the environment. In the further development of the helicopter construction, these noise emissions and vibrations shall be significantly reduced. One development in this regard involves the use and the operation of a flap on the lift generating blade. The pivotable flap is arranged in the area of the profile leading edge and/or the profile trailing edge of the blade, where the flap is pivotally arranged about its pivot axis.
The application of a flap in or on the rotating rotor blade of a rotary wing aircraft is clearly distinguished from the flaps of a rigid wing of a fixed wing aircraft. These two fields of application cannot be overall or globally compared with one another. The flap in the rotating rotor blade is subjected to unusually strong loads or demands. These loads or demands with respect to the flap result from
vibrations of the rotating rotor blade,
dynamic loads from the centrifugal force on the rotating rotor blade, and
dynamic loads as a result of effective aerodynamic forces.
This observation applies for basically all structural components or assemblies that are connected with the rotor blade.
The published European Patent Application EP 1,035,015 A2, paragraphs 0036 and 0037, describes a flap drive with a flap, which are installed in a rotor blade, and an electrical regulating or control arrangement for the flap drive. The flap drive consists of a piezoactuator, and a movable link frame coupled with the piezoactuator. The link frame is connected by force transmission means with the pivotally supported flap. The piezoactuator is secured on one side on the inner structure of the blade, and the flap is pivotally supported in the structure of the blade. At the time of manufacturing the rotor blade, simultaneously also the flap drive and the flap must be installed in the rotor blade. The piezoelement, as the central core element of a piezoactuator, takes over the function of an actuator member, which can adjust the flap from a base or initial position along a displacement path or a prescribed adjustment angle. The actuating or adjusting signal (adjusting value Y) is received by the piezoactuator from the electrical control arrangement.
The known control arrangement is connected with measuring elements. One measuring element senses the angle of the flap adjustment. That corresponds to the control output value, which is fed back to the control arrangement as a feedback value. In this known arrangement, any bearing play that may be present in the frame construction of the actuator can be counteracted or compensated in view of the feedback signal. However, the force/displacement dependence of the piezoelement is thereby not removed or regulated-out. The known technical solution also does not describe how the control arrangement can react to interference values which result from the above described demands that act on the flap. Interference values cannot satisfactorily be regulated-out or compensated.
In the use of a piezoactuator as an actuating or adjusting element, it is known that a strict proportionality exists between the applied electrical voltage and the strain elongation of the piezoactuator. Due to this constant dependence, it is known to regulate or control the required angular adjustment of the flap by controlling an electrical voltage that is to be applied to the piezoactuator. That makes the control arrangement. Thus, in the following discussion, a flap drive with a piezoactuator will be considered.
In practice it has been found, however, that an exclusive regulation or control of the angle of the flap does not achieve the desired results. This is caused by a plurality of influences or effects, which interferingly influence the adjustment of the flap.
Such influence values are aerodynamic forces, for example caused by the flow around the rotor blade, the variation of the incident flow of the rotor blade, effective air vortices, trailing vortices as a result of blade vortex interferences, in short called BVI (blade vortex interaction), as well as mechanically active influence values such as the bearing friction, and the time variation of the bearing friction of the flap bearings or of the bearings in the flap drive. Some of these influence values (also called interference values) act on the flap in a highly dynamic and rapidly varying manner.
These interference values are not foreseeable or predictable and are quantitatively difficult to determine. A high dynamic of the interference values also requires a high frequency (approximately 50 to 100 Hz) of the actuating manipulation which regulates-out the interference values relative to the flap. Dynamically acting interference values have previously been neglected in the prior art in connection with the regulation or control of a flap. Due to these technical difficulties, it is problematic to embody a precisely functioning regulation or control. An iterative optimization of the adjusting or actuating value, or the search for an actuator (adjusting element) with other functional characteristics, does not achieve improved results.
In view of the above, it is an object of the invention to develop a regulation or control method and the corresponding regulating or control arrangement, in order to ensure a precise adjustment in all necessary angular positions of a flap in the rotor blade of a helicopter during the flight operation thereof. The invention further aims to avoid or overcome the disadvantages of the prior art, and to achieve additional advantages as apparent from the present specification.
The above objects have been achieved according to the inventive method, in that a measuring element senses or detects the actuating force on the force transmission means between the piezoactuator and the flap, the actuating force signal is provided as a measurement signal to a servo following controller that is subordinated to the primary control arrangement, the servo following controller receives the controller output value of the primary control arrangement as a reference value, the servo following controller then forms a controller output value that is provided to the piezoactuator, and the flap angle set-point or nominal value transducer of the control arrangement receives a pre-setting of the nominal value from an external regulator or controller.
The above objects have further been achieved according to the inventive apparatus, in that a measuring element is arranged on the force transmission means and is connected with a controller subordinated under the primary control arrangement, this controller is connected with the piezoactuator, and the control arrangement is connected with an external controller by means of a set-point or nominal value transducer. In a further embodiment, the force measuring element is a strain gage. This measuring element provides a corresponding electrical measurement signal in a feedback loop to the controller that regulates the force measurement value and that operates as a servo following controller with respect to the control arrangement.
The invention makes it possible to effectively regulate-out highly dynamically effective aerodynamic forces as well as friction forces in the mechanism of the force transmission to the flap and in the flap bearing support. These interference values are regulated-out in real time. This is achieved in that the invention does not wait until the control difference between the actual flap angle and the rated or desired flap angle triggers a control arrangement that regulates the angle measurement value to carry out the intended adjusting manipulation, but instead the invention provides an additional immediate regulation or control of a force measurement value in a servo following controller. Thereby, the actuating value of the angle control of the master or reference controller can be maintained.